1. Field of the Invention
The present invention generally relates to the field of creating diamine salts of a free form of 5-sulfoisophthalic acid and for using those salts in treating nylon polymers.
2. Description of Related Art
Nylon is a frequently used polymer, present in carpet fibers, clothing, fishing lines, parachutes, footwear, pantyhose, toothbrush bristles, Velcro, airbags, printing plates, rope, guitar strings, racquet strings, flexible tubing, and basketball nettings, among other things. Nylon, as it is known in the art, is comprised of repeating units linked by amide bonds into monomers, which are then reacted to form long polymer chains, and is therefore also known as polyamide (“PA”). More specifically, the copolymers are formed by reacting equal parts of a diamine and a dicarboxylic acid, so that amide bonds form at both ends of each monomer. Longer polymers are achieved by creating a solid nylon salt at room temperature with a 1:1 acid-base ratio, which polymerizes at 285 degrees Celsius. Nylon can be made in several forms, including nylon 6,6; nylon 6; nylon 9; nylon 5,10; nylon 6,11; polymers with added diacids; and copolymers of these forms. Those in the art may also refer to these compounds as PA66, PA6, etc. As used herein, the term “nylon” encompasses all polyamides known to those skilled in the art or yet to be discovered.
A particularly prevalent use of nylon is as nylon fiber. While defined by the Federal Trade Commission as “a manufactured fiber in which the fiber forming substance is a long-chain synthetic polyamide in which less than 85% of the amide-linkages are attached directly (—CO—NH—) to two aliphatic groups,” the term herein is used more broadly to encompass any fiber comprised of any polyamide and currently, or in the future, used in a textile.
Nylon fiber is particularly useful in carpet, and is believed to be the most commonly used fiber for carpet. This is because of its many advantages: nylon can be dyed topically or in a molten solution; is easily printed; is very durable; is abrasion-resistant; and is resistant to insects, fungi, molds, mildew, and rot. When blended with wool, it increases the carpet's durability and lowers its cost.
Nylon fibers contain many dye sites in the form of amide linkages. These sites may be filled by acidic dye molecules in order to color the polymer and ultimately the carpet. If left unfilled, the fiber can be prone to staining by acidic substances such as soft drinks, coffee, and wine.
One current way of making nylon fibers more resistant to acid dye stains is to include monomers with sulfonate moieties in the polymers. However, these sulfonate-containing compounds have higher melt viscosities that reduce the effectiveness of the melt spinning process by which nylon fibers are generally prepared, because polymerization is slower and because the polymerized nylon cannot be removed from the polymerizing machinery as easily. The sulfonate elements can also act as surfactants, which create foam during the polymerization process, and thereby disrupt the product's ultimate uniformity. Finally, the sulfonates attract water molecules, making the final product require more time to dry. In addition, polymers with sulfonate-containing monomers achieve poor stain resistance and only moderate soil resistance. Accordingly, there is a need in the industry for a method of making nylon acid-resistant which does not include sulfonate-containing monomers.
Another common way of achieving stain resistance and rapid drying is by applying a compound to the nylon fiber that acts as a topical “stain blocker” by associating with, and thereby blocking access to, the acid dye sites. Such compounds themselves also do not associate with the acid dye. One known current topical dye site blocker is sulfonated aromatic condensates. However, these compounds are only temporary and are removed from the textile or carpet during normal use, maintenance, and cleaning, even with regular detergent. These compounds are also not adequately resistant to light, nitrous oxides, and bleach, and may also alter the treated nylon fiber's colors. It is therefore desirable in the industry for a compound which has the ability to permanently impede acid dye sites, be resistant to environmental conditions such as light and detergents, and not alter the treated fiber's colors.
Another currently used molecule in treating nylon-based textiles is metal salts of sulfoisophthalic acid (“SIPA”). The acronym “SIPA” can describe a molecule with the formula of (RO(O)C)2ArSO2OM, in which each R can be the same or different, and is hydrogen or an alkyl group containing 1 to about 6 carbon atoms or hydroxyalkyl group containing 1 to 5 carbon atoms; Ar is a phenylene group; and M is hydrogen, an alkali metal, an alkaline earth metal, diamine, or combinations of two or more thereof. Of particular use in treating nylon-based textiles are the lithium and sodium SIPA salts (“LiSIPA” and “SSIPA”). Use of such metal salts in treating nylon carpet fabrics is disclosed in U.S. Pat. No. 6,334,877, to Studholme, and U.S. Pat. No. 3,475,111, to Meyer.
The presence of lithium and sodium cations, i.e., sodium or lithium SIPA salts as intermediates, in LiSIPA and SSIPA however can be problematic. They are believed to interfere with the manufacturing process, in that they contribute to a precipitate that clogs the polymerizing machinery. Sodium is believed to be particularly problematic in this regard. It is therefore desirable in the industry for the development of a metal salt of SIPA used in treating nylon that has a cation that does not precipitate in a manner detrimental to the manufacturing process.
Another problem with current metal salts of SIPA is the presence of sulfates, which, especially in the presence of lithium or sodium, is believed to generate an inorganic buildup. This buildup interferes with heat transfer, which lowers the efficiency of the manufacturing process. It also necessitates more frequent cleaning, which lowers the amount of time that can be spent manufacturing the product and requires man hours for such cleaning, which both in turn contribute to a higher cost of manufacturing the final product. It is therefore desirable in the industry for the development of a metal salt of SIPA that can be generated in a manner that minimizes the presence of sulfates.
Current production processes of these metal salts of SIPA generate the salt of SIPA. However, these current processes do not isolate the salt formed between the diamine and acid, but instead isolate and use SSIPA. Given the lingering presence of a sodium cation, these processes do not solve the aforementioned problem of sodium-based precipitates.
Another current process charges a reaction unit with deionized water, then SSIPA, in order to make a solution. The solution is then charged with 80% hexamethylene diamine (“HMDA”) in 20% water, after which the HMDA replaces the sodium as the cation. This process does achieve the stated goal of producing a SIPA salt without sodium as its cation. However, this process generates a good deal of free sodium ions when the HMDA replaces sodium as the salt's cation. This results in a large amount of sodium present in the solution which, as explained above, can adversely affect the polymerization process by precipitating. It is therefore desirable for the final HMDA salt to be generated without the sodium salt of SIPA as an intermediate. It is also desirable, for the sake of efficiency and lowering the amount of raw materials used, to eliminate superfluous steps in processes for manufacturing HMDA-SIPA.
U.S. Pat. No. 3,475,111 to Meyer mentions preparing the 1:1 HMDA salt of SSIPA for use in occupying nylon acid dye sites. However, Meyer does not disclose a salt with one or three HMDA molecule(s) to two SIPA molecules, nor does it disclose any method or process of preparation of any form of a HMDA salt. It is believed that the 1:1 salt is more difficult to isolate than the 1:2 salt, as it is less prone to crystallization and is much more soluble. The 1:2 salt is therefore believed be more desirable, for those in the industry as it is more accessible. Therefore, there remains a need in the industry for the ability to generate a readily isolated HMDA salt of a SIPA without generating precipitates that adversely affect the manufacturing process.